There is a continuing trend in recent years to undertake research and development efforts for recycling waste cooking oil like edible oil and fat as well as mineral oil like engine oil, which have been disposed of as waste products by food industries and homes, as raw materials of diesel engine fuel from a viewpoint of conservation of resources and environmental conservation.
For example, methods for using waste cooking oil as a raw material of diesel engine fuel thus far proposed include techniques for methyl-esterifying the waste cooking oil through a reaction with methanol, mixing resultant fatty acid methyl ester with light oil at a specific ratio and then using oil thus produced as fuel oil for diesel engines, or as bio-diesel fuel (refer to Patent Documents 1 and 2).
The bio-diesel fuel thus obtained produces smaller amounts of toxic exhaust gases like black smoke and attracts attention as fuel that poses a lesser environmental burden.
Another method proposed, on the other hand, is to simply mix waste cooking oil or mineral oil with petroleum-based fuel oil and use resultant mixed oil as diesel engine fuel.